1. Field of the Invention
The present invention relates to an image reading apparatus.
2. Related Background Art
An image processing apparatus is known in which either a recording head or a scanner unit is mounted on a carriage and which records image data from a computer on recording paper while cooperating with a paper conveying system or reads image data recorded on an original.
The image processing apparatus adopts a recording system, such as an ink-jet recording system, a dot-impact recording system, or a thermal transfer recording system. When outputting image data onto recording paper, the recording head is attached to the carriage, which is reciprocated to record the image data on the recording paper. On the other hand, when reading the image data of an original, the scanner unit is mounted on the carriage instead of the recording head, and the carriage is reciprocated to perform image data reading processing.
In such an image processing apparatus, the distance between the original and the scanner unit is first adjusted by using, for example, a white reference sheet. After adjusting the distance between the original and the reference sheet, image data is read on a predetermined pixel region basis, which is a band unit. That is, when reading image data in the monochrome mode, one band (for example, 256 pixels) of image data is read by using a green light source. When reading image data in the full color mode, one band of image data, which is successively irradiated with lights from a red (R) light source, a green (G) light source, and a blue (B) light source, is read successively. The read image data is stored in a memory unit, and then transferred to an information processing apparatus, such as a host computer.
It is to be noted, however, that the distance between the original image and the scanner unit, which is adjusted in advance as stated above, is subject to variation depending on the kind of original, which may be a cut paper sheet, a photograph, a postcard, etc. Thus, when reading image data recorded on an original which is of a type different from the reference sheet, a so-called “band unevenness” is generated, resulting in a deterioration in the quality of the image read.
In view of this, an overlap reading is performed in which a predetermined lower region of one band that can be read by one scanning is overlapped with a predetermined upper region of the next band.
However, even when the above-mentioned overlap reading is performed, the reading processing can take an excessively long time depending on the kind of original, recording mode, etc. since the band width that allows reading by one main scanning, the band region subjected to overlap reading, etc. are set independently of the kind of original, reading mode, etc.